The present application claims the benefit of priority from Israel Patent Application No. 143006 filed May 7, 2001, the contents of which are incorporated herein by reference.
The present invention relates to antennas, specifically electronically steered planar array antennas. More specifically, the present invention relates to antennas that can, in the presence of a large electrically conductive plate, provide undegraded beam steering at any desired polarization, in planes perpendicular to, and at low elevation angles above the conductive plate.
One example is a Luneberg hemispherical lens antenna mounted on top of a metal-plane plate, as shown for example in C. H. Walter et al. xe2x80x98Surface wave Luneberg lens antennaxe2x80x99, U.S. Pat. No. 3,255,454 and in xe2x80x9cDBS-2400 In-Flight TV Antenna Systemxe2x80x9d, Product Information Sheet, Datron/Transco Inc., 200 West Los Angeles Avenue, Simi Valley, Calif. 93065 (hereinafter DBS2400). This antenna arrays 4 Luneberg hemispherical lenses for higher antenna gain, which is further enhanced by virtue of reflections from the ground plane. The DBS2400 antenna provides electronic polarization setting (via control of feed element polarization) and mechanical beam steering in azimuth (rotation of metal-plane plate) and in elevation (movement of feed elements in elevation around the hemispherical lenses).
Electronic beam steering may be applied to a Luneberg hemispherical lens antenna unit, but this requires the incorporation of a switch network that selects one or a group of adjacent feed elements from a concave spherical feed array that covers a partial sector of the hemispherical Luneberg lens. In addition, when an array of lenses is used for gain enhancement (DBS-2400), electronic beam steering in azimuth will be limited by gain degradation due to mutual lens blockage.
A second example for a steered beam gain enhanced antenna lying on top of an electrically conductive ground plane is the Cylindrical Ray Imaging Steered Beam Array (CRISBA) antenna described in co-pending published U.S. patent application No. 2002/0163480 by the present inventor. The antenna described therein features modularly tailored directive gain, and lends itself to electronic beam steering in azimuth and in elevation, and in addition allows electronically controlled polarization setting. However, the cylindrical geometry of the CRISBA antenna trades antenna gain performance at low elevation angles above the ground plane for better gain performance at higher elevation angles. If wider elevation coverage is not essential, an antenna of planar geometry of the same height above the ground plane should provide higher gain.
Thus, very few prior art antennas in general, and no planar array antennas in particular, can provide undegraded beam steering at any desired polarization, in planes perpendicular to, and at low elevation angles above the conductive plate are of planar array geometry.
It would therefore be beneficial to have a low-profile, cost-effective polarization-controlled, steered-beam antenna of planar geometry that achieves modularly tailored high directive gain at low elevation angles above a large electrically conductive ground plane on top of which it is mounted.
The present invention discloses an innovative planar, ray-imaging, electronically-steered array antenna, whose radiating array elements are disposed on a planar surface sector above an electrically conductive ground plane that enhances the antenna gain. The antenna of this invention is to be mounted over, and perpendicular to, a large metal ground plane, and provide high directive gain at low elevation angles above the ground plane. The conductive ground plane forms an integral part of the antenna, and the required dimensions of this ground plane depend on the array height, and on the lowest elevation coverage angle from the possibly tilted) ground plane. The antenna of the present invention is further characterized by a modular design that tailors the required antenna gain and azimuthal directivity through the stacking of identical antenna segments side by side. The antenna of the present invention is unique in that it can generate, with the aid of a multiple-beam microwave network or a two-ended series-feed network, a pair of symmetrically steered beams from an incident wavefront received by a linear (column) or planar array, in conjunction with reflections from a bottom metal plate. The coherent combination of the pair of symmetrically steered beams with the reflections allows an effective doubling of the antenna aperture in elevation.
According to the present invention there is provided, in a first preferred embodiment, a ray-imaging, electronic beam-steering antenna comprising at least one antenna segment, each antenna segment having at least one output and including a plurality of horizontally-polarized radiating column-array elements and an elevation beam-forming assembly, the plurality of radiating column-array elements disposed adjacently perpendicular to an electrically conductive ground reflector plane, the ground reflector plane allowing gain-enhanced, horizontal-polarization beam generation and steering in planes perpendicular to the ground reflector plane, whereby the antenna is electronically steerable in elevation, or both in elevation and in azimuth.
According to one feature of the first preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a microwave multiple-beam network having a first plurality of element ports and a second plurality of beam ports, a set of two-way power dividers, each of the set having a pair of output ports and incorporating an 180xc2x0 phase shift between two ports of the pair of output ports, and a set of two-way power combiners, each of the set having a pair of input ports and incorporating an 180xc2x0 phase shift between two ports of the pair of input ports, and a beam selection switching module connected to the set of power combiners.
According to another feature of the first preferred embodiment of the antenna of the present invention, the microwave multiple-beam network is a Butler type matrix.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, the Butler type matrix is selected from the group consisting of stripline printed circuits and microstrip printed circuits microwave matrices.
According to another feature of the first preferred embodiment of the antenna of the present invention, the microwave multiple-beam network is a Ruze-type or Rotman-type lens.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, the beam selector switching module includes a single-pole switching module that incorporates a passive beam conversion matrix.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, the beam selection switching module includes a two-pole switch module, whereby the two-pole switch module allows both single pole selection and dual pole selection.
According to the present invention, the first preferred embodiment of the antenna of the present invention further comprises a power combiner connected electrically to the outputs of at least two antenna segments, and selected from the group consisting of a conventional power combiner, a power combiner having phase shifters, a power combiner having delay phase shifters, a Ruze-type lens, a Rotman-type lens, and any combination thereof.
According to another version of the first preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a double ended series feed network or a double ended leaky wave structure and a two-way power combiner that incorporates a 180xc2x0 phase shift at one of its input ports.
According to the present invention, there is provided, in a second preferred embodiment, a ray-imaging, electronic beam-steering antenna comprising at least one antenna segment, each antenna segment having at least one output and including a plurality of vertically-polarized radiating column-array elements and an elevation beam-forming assembly, the plurality of radiating column-array elements disposed adjacently perpendicular to an electrically conductive ground reflector plane, the ground reflector plane allowing gain-enhanced, vertical-polarization beam generation and steering in planes perpendicular to the ground reflector plane, whereby the antenna is electronically steerable in elevation, or both in elevation and in azimuth.
According to one feature of the second preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a microwave multiple-beam network having a first plurality of element ports and a second plurality of beam ports, a set of two-way power dividers, each of the set of power dividers having a pair of output ports, a set of two-way power combiners, each of said set of power combiners having a pair of input ports, and a beam selection switching module connected to the set of power combiners.
According to another feature of the second preferred embodiment of the antenna of the present invention, the microwave multiple-beam network is a Butler type matrix.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the Butler type matrix is selected from the group consisting of stripline printed circuits and microstrip printed circuits microwave matrices.
According to another feature of the second preferred embodiment of the antenna of the present invention, the microwave multiple-beam network is a Ruze-type or Rotman-type lens.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the beam selector switching module includes a single-pole switching module that incorporates a passive beam conversion matrix.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the beam selection switching module includes a two-pole switch module, whereby the two-pole switch module allows both single pole selection and dual pole selection.
According to the present invention, the second preferred embodiment of the antenna of the present invention further comprises a power combiner connected electrically to the outputs of at least two antenna segments, and selected from the group consisting of a conventional power combiner, a power combiner having phase shifters, a power combiner having delay phase shifters, a Ruze-type lens, a Rotman-type lens, and any combination thereof.
According to another version of the second preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a double ended series feed network or a double ended leaky wave structure and a two-way power combiner.
According to the present invention there is provided, in a third preferred embodiment, a ray-imaging, electronic beam-steering antenna comprising at least one antenna segment, each antenna segment having at least one output and including a plurality of dual-polarized radiating column-array elements and an elevation beam-forming assembly, the plurality of radiating column-array elements disposed adjacently perpendicular to an electrically conductive ground reflector plane, the ground reflector plane allowing, for any polarization, gain-enhanced, beam generation and steering in planes perpendicular to the ground reflector plane, whereby the antenna is electronically steerable in elevation, or both in elevation and in azimuth.
According to one feature of the third preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a microwave multiple-beam network, a set of 0xc2x0/180xc2x0 hybrid couplers that symmetrically feed the element ports and beam ports of the multiple-beam matrix, and a pair of beam selection switching modules connected respectively to xe2x80x9csumxe2x80x9d and xe2x80x9cdifferencexe2x80x9d ports of the sub-set of 0xc2x0/180xc2x0 hybrid couplers that feed the beam ports of the multiple-beam network.
According to another feature of the third preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly further includes a complex weighting module connected to the pair of beam selector switching modules.
According to another feature of the third preferred embodiment of the antenna of the present invention, the microwave multiple-beam network is a Butler type matrix.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, the Butler type matrix is selected from the group consisting of stripline printed circuits and microstrip printed circuits microwave matrices.
According to another feature of the third preferred embodiment of the antenna of the present invention, the microwave multiple-beam network is a Ruze-type or Rotman-type lens.
According to the present invention, the third preferred embodiment of the antenna of the present invention further comprises at least one power combiner connected electrically to the outputs of least two antenna segments, the power combiner selected from the group consisting of a conventional power combiner, a power combiner having phase shifters, a power combiner having delay phase shifters, a Ruze-type lens, a Rotman-type lens, and any combination thereof.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, each of the pair of beam selector switching modules includes a single-pole switching module that incorporates a passive beam conversion matrix.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, each of the pair of beam selector switching modules includes a two-pole switch module, whereby the two-pole switch module allows both single pole selection and dual pole selection.
According to another version of the third preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a pair of feed networks having a plurality of output ports, and a complex weight module, connected to the output ports of the pair of feed networks.